REM sleep behaviour disorder in narcolepsy

Narcolepsy is characterized by excessive daytime sleepiness, cataplexy, sleep paralysis and hypnagogic hallucinations. The aim of the study was to evaluate the incidence of REM sleep behaviour disorder (RBD) in consecutive patients with narcolepsy referred to our sleep disorders centre.Among patients examined because of hypersomnia, a diagnosis of narcolepsy was established in 30 patients (mean age 34.1 +/-13.6; 13 females, 17 males) on the basis of clinical features, polysomnography (PSG) and Multiple Sleep Latency Test. Polysomnographic analysis included assessment of muscle activity during REM sleep, recorded from chin and anterior tibialis muscles. Video recordings were reviewed for intense motor activity during REM periods, manifested as excessive, violent body movements (especially legs) and vocalization, reflecting dream-enacting behaviour. Questions about RBD symptoms were asked as a standard in all newly diagnosed patients and those reporting for follow-up visits.Symptomatic, polysomnographically documented RBD was found in three patients. In one of them RBD symptoms appeared during anticataplectic treatment with antidepressive medications. Disturbances of muscle tone regulation during REM sleep without clinical symptoms were found in polysomnography in a further four patients. Among patients reporting for follow-up visits, three subjects confirmed clinical symptoms corresponding to RBD of various severity.RBD occurs in narcolepsy more frequently than it was previously considered. Questions about symptoms of this disorder that may be injurious for the patient or patient's bed partner should be routinely asked during the clinical interview.